A wide variety of techniques concerning the production of photo-sensitive materials have heretofore been developed. These techniques include a method of matting the obverse side or reverse side of photo-sensitive materials to prevent them from taking on an electrostatic charge, aid in eliminating adhesion between the materials and to improve their vacuum adhesion properties.
For example, in a photographic process comprising placing a film original on a photographic light-sensitive material and exposing the photo-sensitive material to light through the film original at the exposure step thereof to form the desired image or pattern in the photo-sensitive material, it is necessary to bring the film original into intimate contact with the surface of a photo-sensitive layer of the photo-sensitive material to eliminate blurring of the exposed image or pattern due to the clearance between them. For this reason, in general, a method utilizing a printing frame is employed. In such a method the photographic light-sensitive material and the film original are placed in a superposed relation between a glass plate and a rubber sheet of the printing frame. The clearance between the glass plate and the rubber sheet is then evacuated to bring the photographic light-sensitive material and the film original into intimate contact with each other. (This method is hereinafter referred to as a "vacuum adhesion method".) Japanese patent application (OPI) No. 111102/76 (corresponding to U.S. Pat. Nos. 4,216,289 and 4,288,326; the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a method of matting a photo-sensitive layer by providing therein a fine pattern consisting of coated areas and uncoated areas, greatly shortening the time required for vacuum adhesion. Matting methods of this type, i.e., methods of forming such fine patterns in a photographic light-sensitive material, are described in, for example, Japanese patent application (OPI) Nos. 96604/76, 98505/76 and 12974/80 (corresponding to U.S. Pat. No. 4,216,289 and 4,288,526, and British Pat. No. 2,025,646A, respectively).
In recent years, among photographic light-sensitive materials, a photo-sensitive material of the type having both surfaces coated with the respective photo-sensitive layers, i.e., a so-called pre-sensitized printing plates which have photo-sensitive layers on both surfaces of the plates, have been increasingly used. In these photographic light-sensitive materials, however, various problems are encountered in providing a fine pattern on the surfaces of the two photo-sensitive layers by a gravure coating method as described in U.S. Pat. No. 4,216,289. For example, it is necessary that a fine pattern is first coated on one surface and dried, and then another fine pattern is coated on the other surface and dried. This method requires the use of relatively large sized equipment. Furthermore, coated areas of the fine pattern provided on the reverse side by the above-described method are sometimes peeled apart or collapsed because they are often rubbed by a conveyer roller before the photo-sensitive material is cut in the desired size. This gives rise to the problem that the vacuum adhesion time required when the photo-sensitive layer on the reverse side is exposed imagewise is seriously increased compared with the time required for imagewise exposing the photo-sensitive layer on the obverse side. Another problem is that in bringing the photo-sensitive layer on the obverse side into intimate contact with a film original by vacuum adhesion and exposing them to light the coated areas of the fine pattern on the reverse side are pressed and collapsed by a printer. This increases the vacuum adhesion time required for exposing the photo-sensitive layer on the reverse side.
In order to overcome the problem of contamination of a film original by a coating layer which is provided to improve vacuum adhesion properties, U.S. Pat. No. 4,288,526 discloses a method of coating a dispersion of a wax-like or fine powdery resin having releasing properties in a low boiling organic solvent by means of an air spray coater. This coating layer easily separates, and also produces problems as described above, because its adhesion force to the surface of a photo-sensitive printing plate is poor. Further, from a viewpoint of safety, it is not desirable to use such organic solvents.
British Pat. No. 2,025,646A discloses a method in which a solid powder is sprayed on a photo-sensitive printing plate and firmly fixed thereto by heating. In the case of a pre-sensitized printing plate, having both surfaces with the respective photo-sensitive layers, the matted layer on one side is collapsed when the photo-sensitive printing plate is conveyed by means of rollers until the sprayed solid powder is cooled after it is heat-adhered. It is, however, difficult from a viewpoint of handling to convey the photo-sensitive printing plate without the use of rollers. Further, in order to produce such powders it is necessary for the resins to be pulverized and classified. This increases production costs.
U.S. Pat. No. 4,288,521 discloses a method of uniformly spraying and adhering a solid powder on the surface of a continuously running photo-sensitive printing plate. This method requires the use of a pressurized air-supply unit, a powder-supply unit, an ejector, a distributor, a cyclon, and so forth. Thus, the equipment for use in this method is very complicated and large. Furthermore, in the case of pre-sensitized printing plates which have photo-sensitive layers on both surfaces of the plate, when the pre-sensitized printing plate is conveyed after simultaneous attachment of solid powder, the solid powder easily separates from the pre-sensitized printing plate.
Photographic light-sensitive materials are matted not only to improve vacuum adhesion properties, but also to prevent electrostatic charging, and sticking and bonding between the photographic light-sensitive materials, although the above explanation has been made by reference to the improvement of vacuum adhesion properties. Application of matting is not limited to the surface of a photo-sensitive layer. The reverse side surface may also be matted. Also, in performing the matting procedure for the purpose of preventing electrostatic charging, or sticking and bonding between photographic light-sensitive materials, the same problems as encountered in improving the vacuum adhesion properties arise.
The present invention is intended to overcome the above-described problems by utilizing an improved electrostatic spray-coating technique for matting.
As is well known, various electrostatic spray-coating processes have been developed, including a disc type coating head, a bell type coating head, and a gun type coating head. In accordance with any of the above-described processes, when an aqueous solution as described hereinafter is electrostatically sprayed and provided on the surface of a photo-sensitive material, if the charged droplets of the aqueous solution have a very small diameter, their adhesion force is poor since the contact area between the surface of the photo-sensitive material and the droplet is small. Therefore, when, after the removal of water in the fine droplets attached, the photo-sensitive material is conveyed while holding it in contact with, for example, rolls, attached fine droplets will separate from the photo-sensitive material as for the cases of the above-described methods, and the desired vacuum adhesion time cannot be attained. Further, the case of photographic light-sensitive material, when the photographic light-sensitive material is brought into intimate contact with a film original, the above-separated droplets or particles deposit on the film original, decreasing its function and dot depth. In particular, in the case of a pre-sensitized printing plates which have photo-sensitive layers on both surfaces of the plate, attached particles on the reverse side surface which are to be exposed later are pressed and collapsed by a printer when the obverse side is brought into contact with the film original by vacuum adhesion and exposed imagewise. This increases the time required for vacuum adhesion for the exposure of the reverse side.